Each cylinder of an internal combustion engine is equipped with one or more gas exchange valves (e.g., intake and exhaust valves) that are cyclically opened during normal operation. In a conventional engine, the valves are opened by way of a camshaft/rocker arm configuration. The camshaft includes one or more lobes arranged at particular angles corresponding to desired lift timings and amounts of the associated valves. The cam lobes are connected to stem ends of the associated valves by way of the rocker arm and associated linkage components. As the camshaft rotates, the cam lobes come into contact with a first pivoting end of the rocker arm, thereby forcing a second pivoting end of the rocker arm against the stem ends of the valves. This pivoting motion causes the valves to lift or open against a spring bias. As the cam lobes rotate away from the rocker arm, the valves are released and allowed to return to their closed positions.
When a cylinder is equipped with more than one of the same type of gas exchange valve (e.g., more than one intake valve and/or more than one exhaust valves), all valves of the same type are typically opened at about the same time. And in order to reduce a number of camshafts, cam lobes, and/or rocker arms required to open the multiple valves, a valve bridge is often used to interconnect the same type of valves with a common rocker arm.
A valve bridge is generally T-shaped, having arms that extend between the stem ends of two like valves. The second end of the rocker arm engages a center portion of the valve bridge, between the arms. With this configuration, a single pivoting motion imparted to the center of the valve bridge by the rocker arm results in lifting of the paired valves by about the same amount and at about the same timing. A lash adjuster can be associated with the valve bridge and used to remove clearance that exists between the valves and corresponding seats (and/or between other valve train components) when the valve is released by the rocker arm. The lash adjuster helps to ensure sealing of the cylinder during the ensuing combustion process.
An exemplary valve bridge is disclosed in U.S. Pat. No. 8,210,144 that issued to Langewisch on Jul. 3, 2012 (“the '144 patent”). Specifically, the '144 patent discloses a T-shaped valve bridge having a center portion and lateral extensions located at opposing sides of the center portion. A bridge cavity is formed within the center portion to receive a lash adjuster, and bores are formed within the lateral extensions to receive stem ends of associated engine valves. The lash adjuster includes a plunger assembled within the bridge cavity to form a hydraulic chamber. The plunger is configured to engage a button member located at an end of a rocker arm and is hydraulically connected to the rocker arm via the button member. A check valve is disposed within the plunger and separates a reservoir chamber from the hydraulic chamber. As pressure within the hydraulic chamber increases, the check valve cuts off fluid communication between the two chambers. As pressure within the hydraulic chamber drops below a pressure of the reservoir chamber, the check valve moves to allow fluid from the reservoir chamber into the hydraulic chamber. A spring is disposed within the hydraulic chamber and configured to bias the plunger out of the bridge cavity.
Although the valve bridge of the '144 patent may be suitable for many applications, it may still be less than optimal. For example, because the valve bridge directly engages the stem ends of the associated valves and the plunger of the lash adjuster, the valve bridge may wear and need to be replaced after a period of operation. This replacement can be expensive in some situations.
The valve bridge of the present disclosure is directed towards overcoming one or more of the problems set forth above and/or other problems of the prior art.